A nicer approach to the use of 'faecal occult blood tests' in assessment of the symptomatic.

Abstract

Faecal occult blood tests, better described as tests for the presence of haemoglobin in faeces, are widely used in asymptomatic population-based screening programmes for colorectal cancer (CRC) as the best available non-invasive initial investigation. However, previously published authoritative guidelines did state that there was no role for these tests in assessment of patients presenting with lower abdominal symptoms in primary care. In consequence, the traditional widely used guaiac-based faecal occult blood test (gFOBT) was eliminated from the repertoires of many laboratories and its use in clinical settings other than screening very much discouraged. New significant controversy has been raised by the recently issued referral guidance for suspected CRC from the National Institute for Health and Care Excellence (NICE) which states that, in possible CRC, patients who do not meet criteria for suspected cancer referral should be offered testing for occult blood in faeces. These recommendations have been subject to significant criticism, in part because the evidence-base was largely founded on the use of gFOBT: these have many well-documented disadvantages throughout the pre-analytical, analytical and post-analytical phases of generation of a result. NICE did note that the recommendation to test for occult blood in faeces would necessitate a change in practice, because such tests are not currently available. It was also recognized by NICE that some evidence suggested that quantitative faecal immunochemical tests (FITs) for haemoglobin might have applicability in triaging symptomatic patients presenting to primary care. There is now significant evidence that FITs do have applicability in assessment of symptomatic patients presenting to primary care, including those who warrant urgent referral, as shown in recent peerreviewed publications, particularly from Scotland and Spain. Although much of the evidence was generated during and after the work on the NICE guidelines was done, it is vital that laboratories are not pressurized into again offering gFOBT to satisfy general practitioner requests made ‘to comply with the NICE guidelines’. Rather, the accumulated evidence is that FIT should be used, ideally using quantitative immunoturbidimetry to measure faecal haemoglobin concentration (f-Hb) with good performance characteristics. It has been shown that use of f-Hb measurements performs better than previous high-risk symptom-based strategies for fast-tracking suspected CRC referrals. Every one of the studies on use of f-Hb at low cut-off concentration in assessment of those presenting with lower abdominal symptoms has shown very high clinical sensitivity (often 100%) for CRC, so that a ‘positive’ test result should stimulate rapid referral for colonoscopy. Moreover and, most importantly, f-Hb in this context has very high negative predictive value (often well over 90%) for the detection of significant colorectal diseases well worthy of detection, namely, CRC, higher-risk adenoma, sometimes precursors of CRC, and inflammatory bowel disease (IBD). In consequence, a ‘negative’ test result provides considerable reassurance that colonoscopy is not required urgently or even at all. There is no doubt that f-Hb